Our long term objective is to identify and characterize proteins that compose and interact with microtubules. Microtubules are essential for cell division, cell structure, and movement of organelles through cells. They are also targets for medically important antifungal and anthelmintic agents and for cancer chemotherapy agents. In spite of the importance of microtubules, many of the proteins that are essential for the functioning of microtubules are unknown and it is our goal to identify some of these proteins. Our general strategy is to identify such proteins by first identifying the genes that encode them and then using the genes to identify and characterize the proteins and determine their functions. We have discovered one such protein, gamma tubulin, and we now wish to test our hypothesis that gmma tubulin functions as a nucleator of microtubule assembly. We will use tbe filamentous fungus, Aspergillus nidulans for our studies because it is an excellent organism for carrying out the molecular genetic and biochemical experiments we propose. Specifically we will 1) create new conditionally lethal mutant alleles of the gamma tubulin gene and determine the effects of these mutations on microtubule assembly in vitro and in vivo, 2) determine if gamma tubulin antibodies or mutations will block assembly of microtubules from microtubule organizing centers and 3) purify and characterize gamma tubulin. To identify additional genes required for microtubule functioning, we propose to use procedures that will allow us to clone genes that encode proteins that co-purify with microtubules, proteins that are components of the microtubule organizing center and proteins that are related to, or interact with, gamma tubulin.